This invention relates to an exhaust silencer structure for outboard motors and more particularly to an improved system for silencing the low speed exhaust gas discharge of such an engine.
As is well known, it is the practice with outboard motors to silence the exhaust gases of the powering engine by discharging them through an underwater exhaust gas outlet and by employing silencing devices within the outboard motor itself for silencing the gases before their discharge through this underwater outlet. However, it is also the practice to discharge the exhaust gases at idle and low speeds through an above the water exhaust gas outlet since the underwater outlet would offer too great a flow resistance under these running conditions. Thus, the discharge of the exhaust gases directly to the atmosphere presents particularly problems in connection with silencing. In U.S. Pat. No. 4,421,490, issued Dec. 20, 1983, and entitled "Exhaust Silencer Structure For Outboard Engines" and assigned to the assignee of this application, there is disclosed an exhaust gas system wherein exhaust gases for low speed are discharged to the atmosphere through a water bath contained within the confines of the motor. Although such devices can offer good silencing, the water bath itself may, if it is the only form of silencing employed, give too high a back pressure.
It is, therefore, a principal object of this invention to provide an improved, effective low speed exhaust gas silencing system for an outboard motor.
It is another object of this invetion to provide a low speed exhaust gas silencing system for an outboard motor that is effective and yet which generates low back pressure.
In connection with the exhaust systems for outboard motors, it has been proposed to use the discharge cooling water of the engine as a means for further improving exhaust silencing and exhaust gas treatment. For example, it has been proposed to add a portion of the discharge coolant water to the exhaust gases to cool them and improve silencing.
It is, therefore, a still further object of this invention to provide an improved cooling system for an outboard motor.
It is a yet further object of this invention to provide an outboard motor cooling system wherein the coolant assists in the exhaust gas treatment.